In a headlight for a vehicle, that is, a so-called low-beam headlight, light higher than a horizontal line is cut in a low beam for preventing an oncoming vehicle or a pedestrian from being dazzled.
Particularly, a luminance intensity distribution in which the light is brighter in a center in a front direction of a road surface in a vehicle travel direction below the horizontal line and reduced above the horizontal line and in the lateral directions is required.
In order to achieve such distribution of light, for example, a lighting device described in Japanese Patent No. 4083516 (Patent Literature 1) is used. The lighting device is shown in FIG. 20.
The lighting device is a so-called multi-eye light including three round lenses 20C, 20C and 20D and four horizontally-long lenses 20A, 20A, 24B and 24B. Seven lights of this light form four types of distributions of light Pa, Pb, Pc and Pd shown in FIG. 21, respectively ranging from narrow to wide in irradiation angle. A low-beam light distribution is formed by superimposing respective lights.
In the related-art lighting device, it is necessary to use a horizontally-long lens or a large-sized lens for forming distributions of light with wide irradiation angles. If a small-sized lens is used, vignetting of light occurs as light is restricted by the size of a lens diameter, which makes formation of distributions of light with wide irradiation angles difficult. There is also a problem that efficiency is reduced when the size is reduced.